It is well known that trace amounts of zinc dissolved in diesel fuel can rapidly accelerate injector nozzle fouling in modern common rail diesel engines. These deposits line the metal surfaces inside the very small holes of the injector nozzle, thereby reducing the fuel flow into the engine which ultimately results in a loss of engine power. According to the study by Leedham et al (“Impact of Fuel Additives on Diesel Injector Deposits,” SAE Technical Paper 2004-01-2935, 2004), trace amounts of zinc (of the order of 1 ppm) in a diesel fuel composition can cause significant power loss (ca. 12%) in a common rail diesel engine when advanced injector nozzles are used.
In general, diesel fuels are known to be prone to zinc pick-up during transportation if exposed to zinc containing components. Conventional wisdom in the art is that it is preferable to avoid any contact between diesel range material and zinc containing systems (see for example, BP Document ADF1403, “Long term storage of diesel”, 2005) either during storage or transportation. It is acknowledged nonetheless, that in non-ideal circumstances, it is possible that contact might occur.
It has been experimentally demonstrated that diesel fuels can pick up zinc in the market logistic system, e.g. if the fuels come into contact with galvanised pipes and fittings; or if diesel fuels to which acid-based lubricity improvers have been added are stored in zinc-containing vehicle fuel tanks. There have been inconsistencies in measurement of the extent of zinc contamination in commercial diesel fuels, largely as a result of uncertainty in the probability of zinc exposure across several studies. However, it is not disputed that the presence of zinc in a market diesel fuel composition at levels even as low as 1 ppm would cause significant injector fouling problems.
Deposit control additives (DCA) have hence been developed to effectively combat zinc-related injector fouling. Many of these additives are also very effective at dissolving the deposits from previously fouled injectors. These deposit control additives appear to act by increasing or facilitating zinc solubility in diesel fuel compositions which typically results in zinc levels in the fuel that are significantly elevated over those where no additive is used. The efficacy of these additives does mean that any potential zinc-induced injector fouling problem can be eliminated, but only if they are used routinely, which result in increased cost. The increase in dissolved zinc in the diesel fuel composition as a result of using the additives could lead to other problems, such as the diesel particulate filter (DPF) operating ineffectively.